AFB problems part 2

Discussion in 'Carter' started by Gulfgears, Sep 8, 2009.

  1. Gulfgears

    Gulfgears Gulfgears

    Ok, adjusted the float level car now starts and runs.
    Put dwell meter on it to set the idle in neutral @ 650, then put in gear to reset idle in gear. Problem is carb has to be set @ 1200 in neutral to idle @ 650 in gear. This can't be right, it'll have to be turning 2000 in neutral to hold 650 in gear with the ac on.

    I know some of you grew up on AFB's so I would greatly appreciate some ideas.

    Oh yes, can't find any vacum leaks either, that would be too easy.

    Thanks in advance
  2. doc

    doc Well-Known Member

    I would bet the farm that you have a vacume leak some where,,, I know that you said that you couldnt find any ,,, but what you are describing is classic for a vac leak....or you are not getting the idle circuit to work right for some reason....could be some stopped up passages in the carb... have you cleaned it and blown out the passages with compressed air????
  3. gag67sky

    gag67sky Member

    Hi, I have the same issue on my 340/4, if I want idle @ 600 in gears(stock set) I have to run around 1500RPM on neutral, way to high I know:shock: .
    I cured all the vacuum leaks, removed carb, disassembled, cleaned, new gaskets, new float needles, can't get better than this at the moment:Dou: .

    Next steps are:
    maybe now I run too rich idle mixture (tend to stall when hot),
    maybe I should give a little more dwell (30 at the moment, stock set but I think I'll try around 30.5/31 as it's worse when I'm 29!)
    maybe then I should give a little more advance (more dwell, less initial advance..)
    I know my idle switch pitch isn't working properly, so I have to increase neutral idle, but not so high I believe????

    Maybe it can help you with your car....

    That's where I'm now, maybe more experienced tell me if I go in the right direction....:Do No:

  4. doc

    doc Well-Known Member

    Do you have stock cams in those engines???? and have you checked the power brake hoses /diaphragms for leaks???
  5. Gulfgears

    Gulfgears Gulfgears

    Well, I've thrown in the towel on this mess! I'm going to find someone who specilizes in rebuilding AFB's. Maybe just buy another one outright.

    Last night I took off all the vacuum hoses, everything, PCV line, power brake hose, distributor hose, connections for transmission and AC. Installed plugs on the carb (airtight) and cranked it up. Ran great, set idle at 600rpms, then watched as idle creeped up to 1200rpms. I then sprayed wd40 around the intake and base of the carb looking for a leak, none found.

    Passed a propane source over the intake and around carb, no changes in speed.

    Decided as has been previously suggested that some circuit inside the carb is screwed up. When I rebuilt the carb every orifice, hole and passage was cleaned out, soaked in carb cleaner and then blown out.

    So, long story, but in this case the carb is most likely the culprit. If it isn't then I can't imagine what else it could be.

    Also this is a bone stock 110,000 mile original engine. No cam.

    Thanks to all for the input, I hope to learn enough to maybe help someone else in the future.
  6. doc

    doc Well-Known Member

    Ok there is one other thing to check before you start spending money and effort,,,,in between the secondary barrels there is a thermal bi metallic spring device that has a rubber v shaped piece that opens and closes with the temp.... is that there and is the rubber part in good shape ????? I think that I remember that back in the day it was called a hot idle is a direct vac leak if it is open.....
  7. Gulfgears

    Gulfgears Gulfgears

    Ok, I'll look tonight. I have a core spare and check both out.

    If that fixes it I'll be both amazed and in your debt.

    Thanks again.
  8. Gulfgears

    Gulfgears Gulfgears

    Hey Doc, the idle compensator thing has a gasket under it.

    Is it possible to make an adapter, put on the old 2 barrel just to see if the problem goes away?

    That way I would know for sure if it's the carb or not.
  9. doc

    doc Well-Known Member

    pm your phone number to me and I will call....
  10. telriv

    telriv Founders Club Member

    When it starts running/idling badly just press down on the idle compensator to see if anything changes.
  11. Gulfgears

    Gulfgears Gulfgears

    Doc & Tom, pressed down on the idle compensator and no change.

    After a lengthy conversation with Doc, I'm thinking my screw up may be by not using Permatex on the intake manifold gaskets when I installed the new manifold.

    I have very little vaacum, as I noticed the power brakes were really hard when I drove the car yesterday. Plus the car has no bottom end and is really sluggish.

    Unless i get this sorted out soon, it looks like I won't be going to "Cruzing the Coast this year. Nuts!!
  12. austingta

    austingta Well-Known Member

    I learned about sealing the intake on my 455 the hard way, by doing it twice.
    Also, put copper sealer spray around the ports.
  13. telriv

    telriv Founders Club Member

    One last thing. Did you install the metal separater/heat shield plate under the carb??? If this is not installed will give you the exact same problems. Just another thought.

    Tom T.
  14. Gulfgears

    Gulfgears Gulfgears

    Yep bought the plate and have a gasket between the plate and the manifold and between the plate and the carb.

    Starting tomorrow I'll be removing the intake and putting new gaskets with permatex and even the spray on copper stuff, just to make sure. Then torque the bolts to 50ft. lbs. in sequence.

    Remount the carb, and see what happens.

    Sure wish there were Buick car guys out here in the country, I could use some extra eyes to make sure it goes right.
  15. doc

    doc Well-Known Member

    just use permatex 300..... that is all you need....
  16. Gulfgears

    Gulfgears Gulfgears

    Well, here's the latest on this saga:

    Pulled intake, cleaned head side gasket surface, cleaned manifold side mating service.

    Applied Permatex, let it dry to tacky state on head side surface and then applied gaskets (FelPro). Applied Permatex to manifold side surfaces. Installed intake manifold and torqued manifold to 50 ft. lbs.

    Took pipe plugs to plug securely all vaccum points on the manifold to make sure I got no leaks.

    Hooked up carb with two new gaskets with Permatex, on gasket on manifold, installed plate, Permatex, then installed second gasket, then installed carb. Tightened carb down.

    Fired it up, and no change. Machine shop guy said to place hand over carb when engine is running and if engine speeds up it's a vaccum leak. Tried this and engine slowed down, so it doesn't appear to be a vaccum leak. I think the carb is terminal.

    Next up is a rebuilt AFB (anybody got a great 4055S) or going to go the Edelbrock route.

    Here's a couple of interesting shots of the missing intake maniold divider. This must have been broken off when the engine was built as this engine is original and has not been rebuilt. Makes you wonder where QC was back in the day!

    Attached Files:

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